Type IV pilin is the major subunit of the pilus or pili which are filamentous structures covering many microorganisms including bacteria and yeast. Among these microorganisms, many pathogenic species express Type IV pilins, including, e.g., P. aeruginosa, N. meningitides, N. gonorrhoeae, Vibro cholera, and Pasteurella multocidam. The first step in infection with these pathogenic microorganisms is adherence to target cells through the pili. In particular, Type IV pilins of Pseudomonas aeruginosa bind to asialoGM1 receptors on epithelial cells (Saiman et al., J. Clin. Invest. 92(4):1875–80 (1993); Sheth et al., 11(4):715–23 (1994); Imundo et al., Proc. Natl. Acad. Sci. USA, 92(7):3019–23 (1995); Hahn, Gene 192(1):99–108 (1997)). Thus, the pili of these microorganisms are a major virulence factor, and result in colonization by pathogenic microorganisms and infections in humans.
For example, Pseudomonas aeruginosa causes between 10% and 20% infections in most hospitals. Pseudomonas infection is common among patients with cystic fibrosis, burn wounds, organ transplants, and intravenous-drug addiction. Pseudomonas infections can lead to serious conditions, such as endophthalmitis, endocarditis, meningitis, pneumonia, and septicemia. In particular, colonization of cystic fibrosis (CF) individuals with Pseudomonas aeruginosa represents a significant negative milestone in the progression of this disease. Once colonized, patients are subject to the damaging effects of various secreted virulence factors and to the inflammatory response of the host immune system.
Type IV pili are composed of pilin polymers arranged in a helical structure with five subunits per turn (Forest et al., Gene 192(1): 165–9 (1997); Parge, Nature 378(6552):32–8 (1995)). The portion of the pilin protein responsible for cell binding is found near the C-terminus (amino acids 122–148) in a β-turn loop subtended from a disulfide bond (Campbell et al., Biochemistry 36(42):12791–801 (1997); Campbell et al., J. Mol. Biol. 267(2):382–402 (1997); Hazes et al., J. Mol. Biol. 299(4):1005–1017 (2000); McInnes et al., Biochemistry 32(49):13432–40 (1993)). For P. aeruginosa, a 12 or 17 amino acid sequence (depending on the strain) in this loop interacts with receptors on epithelial cells. For CF individuals, the overproduction of the R domain of mutant cystic fibrosis transmembrane conductance regulator (CFTR) can lead to an increased level of asialoGM1 and, accordingly, an increased binding of P. aeruginosa (Imundo et al., Proc. Natl. Acad. Sci. USA 92(7):3019–23 (1995); Saiman et al., J. Clin. Invest. 92(4):1875–80 (1993); Bryan et al., Am. J. Respir. Cell Mol. Biol. 19(2):269–77 (1998); Imundo et al., Proc. Natl. Acad. Sci. USA 92(7):3019–23 (1995); Saiman et al., J. Clin. Invest. 92(4):1875–80 (1993)). Functional studies of pilin have indicated that only the last pilin subunit (the tip) of a pilus interacts with epithelial cell receptors (Lee et al., Mol. Microbiol. 11(4):705–13 (1994)).
To date, efforts to produce an effective anti-pilin vaccine have not been very successful. In part, this limited success is because the most immunogenic portion of the protein (the middle) does not generate antibodies that interfere with adhesion. Unfortunately, the C-terminal loop of pilin is not very immunogenic, and high titer responses have only been reported with the use of strategies that employ multiple display copies of the loop sequence (Hahn et al., Behring. Inst. Mitt. (98):315–25 (1997)). For CF patients, strategies to inhibit Pseudomonas colonization are considered an important element in reducing the morbidity normally associated with the development of chronic infections (Tang et al., Infect. Immun. 63(4):1278–85 (1995); Li et al., Proc. Natl. Acad. Sci. USA 94(3):967–72 (1997); Tang et al., Infect. Immun. 63(4):1278–85 (1995) Doig, P. et al., Infect Immun 58(1):124–30 (1990); El-Zaim, H. S. et al. Infect Immun 66(11):5551–4 (1998)).
Accordingly, there is a need to develop compositions for reducing or preventing infections by pathogenic microorganisms including, in particular, Pseudomonas aeruginosa. Embodiments of this invention address this and other needs.